The present invention is directed to colored particles and process for the preparation thereof. More specifically, the present invention is directed to colored particles comprising silica particles containing a water soluble dye entrapped therein, said silica particles being coated with a surfactant. One specific embodiment of the present invention is directed to electrostatic toner compositions comprising a resin and colored particles comprising silica particles containing a water soluble dye entrapped therein, said silica particles being coated with a surfactant. The colored particles of the present invention are also suitable for other applications, such as colorants for plastics, colorants for liquid electrostatic developers, colorants for oil based inks, such as those used in ball point pens and other writing implements, colorants for hot melt ink jet inks, and the like.
Known colorant materials generally consist of pigments or dyes. Pigments generally are particulate colored materials that are dispersed in the material to be colored, whereas dyes generally are compositions which color other materials either by becoming dissolved or dispersed in the material to be colored or by reacting chemically with the material to be colored.
One example of a material that contains a colorant is an electrostatic toner for electrostatic printing processes. The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. Toner typically comprises a resin and a colorant. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Another known process for forming electrostatic images is ionography. In ionographic imaging processes, a latent image is formed on a dielectric image receptor or electroreceptor by ion deposition, as described, for example, in U.S. Pat. No. 3,564,556, U.S. Pat. No. 3,611,419, U.S. Pat. No. 4,240,084, U.S. Pat. No. 4,569,584, U.S. Pat. No. 2,919,171, U.S. Pat. No. 4,524,371, U.S. Pat. No. 4,619,515, U.S. Pat. No. 4,463,363, U.S. Pat. No. 4,254,424, U.S. Pat. No. 4,538,163, U.S. Pat. No. 4,409,604, U.S. Pat. No. 4,408,214, U.S. Pat. No. 4,365,549, U.S. Pat. No. 4,267,556, U.S. Pat. No. 4,160,257, and U.S. Pat. No. 4,155,093, the disclosures of each of which are totally incorporated herein by reference. Generally, the process entails application of charge in an image pattern with an ionographic writing head to a dielectric receiver that retains the charged image. The image is subsequently developed with a developer capable of developing charge images.
Many methods are known for applying the electroscopic particles to the electrostatic latent image to be developed. One development method, disclosed in U.S. Pat. No. 2,618,552, the disclosure of which is totally incorporated herein by reference, is known as cascade development. Another technique for developing electrostatic images is the magnetic brush process, disclosed in U.S. Pat. No. 2,874,063. This method entails the carrying of a developer material containing toner and magnetic carrier particles by a magnet. The magnetic field of the magnet causes alignment of the magnetic carriers in a brushlike configuration, and this "magnetic brush" is brought into contact with the electrostatic image bearing surface of the photoreceptor. The toner particles are drawn from the brush to the electrostatic image by electrostatic attraction to the undischarged areas of the photoreceptor, and development of the image results. Other techniques, such as touchdown development, powder cloud development, and jumping development are known to be suitable for developing electrostatic latent images.
U.S. Pat. No. 4,439,510 (McLoughlin) discloses a method of preparing electroscopic marking particles comprising encapsulating an ink using an aqueous phase emulsion solution including an albumin stabilizer which becomes hydrophobic during processing to give relatively dry, non-tacky particles.
U.S. Pat. No. 4,680,200 (Solc) discloses colloidal size particles of an organic solid such as a pigment that are encapsulated in a hydrophobic addition polymer such as a polymer of styrene by a polymerization process wherein a water-immiscible (hydrophobic) monomer is dispersed in an aqueous colloidal dispersion of the organic particles and subjected to conditions of emulsion polymerization. The resulting encapsulated particles are useful as toners and pigments.
U.S. Pat. No. 4,977,052 (Mikami) discloses an electrostatographic toner material suitably employable for the pressure fixing process, which comprises encapsulated toner particles having an average particle size in the range from about 0.5 to 1,000 microns, in which the toner particle comprises a pressure fixable adhesive core material containing a colorang and a pressure rupturable shell enclosing the core material, said shell being made of a polymer selected from the group consisting of polyurethane, polyurea, and polythiourethane. The patent also discloses a process for preparing the toner material.
U.S. Pat. No. 3,691,090 (Kitajima et al.) discloses a process for the preparation of capsules containing a core material which comprises dispersing the core material in a solution of an organic solvent and an encapsulating material, dispersing the dispersion in an aqueous inorganic salt solution, and then removing the organic solvent.
U.S. Pat. No. 4,409,039 (Lepesant et al.) discloses a high stability printing liquid intended for ink jet printing which is in the state of a microemulsion formed by a dispersing phase containing a group of intercompatible constituents and a dispersed phase containing a second group of intercompatible constituents, the constituents of the first and second groups being incompatible with one another. The two phases are separated by an interfacial liquid containing surfactant molecules in such a way that the dispersed phase is in the form of globules of 500 to 1,000 Angstroms.
U.S. Pat. No. 4,840,674 (Schwarz) discloses an improved ink composition comprising a major amount of water, an organic solvent selected from the group consisting of tetramethylene sulfone, 1,1,3,3-tetramethyl urea, 3-methyl sulfolane, and 1,3-dimethyl-2-imidazolidone, which solvent has permanently dissolved therein spirit soluble dyes such as black, yellow, cyan, magenta, brown, and mixtures thereof.
U.S. Pat. No. 4,877,451 (Winnik et al.) discloses an ink jet ink composition which comprises water, a solvent, and a plurality of colored particles comprising hydrophilic porous silica particles, to the surfaces of which dyes are covalently bonded through silane coupling agents. The particles are prepared by a process which comprises reacting hydrophilic porous silica particles with a silane coupling agent in the absence of water to form particles having covalently attached thereto coupling agents, followed by reacting a dye with the coupling agent attached to the silica particles.
U.S. Pat. No. 4,879,199 (Moffat et al.) discloses a process for controlling the electrical characteristics of colored toner particles. The process comprises preparing a first core material comprising first pigment particles, core monomers, a free radical initiator, and optional polymer components, preparing a second core material which comprises second pigment particles, core monomers, a free radical initiator, and optional polymer components, said second pigment particles being of a different color from that of the first pigment particles, encapsulating separately the first core material and the second core material within polymeric shells by means of interfacial polymerization reactions between at least two shell monomers, of which at least one is soluble in aqueous media and at least one of which is soluble in organic media, wherein the polymeric shell encapsulating the first core material is of substantially the same composition as the polymeric shell encapsulating the second core material, and subsequently polymerizing the first and second core monomers via free radical polymerization, thereby producing two encapsulated heat fusible toner compositions of different colors with similar triboelectric charging characteristics.
P. Espiard et al., "A Novel Technique for Preparing Organophilic Silica by Water-In-Oil Microemulsions," Polymer Bulletin, vol. 24, pages 173 to 170 (Spring 1990), the disclosure of which is totally incorporated herein by reference, discloses a technique for preparing ultramicro spherical silica particles containing vinyl groups on their surfaces by a combination of the sol-gel technique and the water-in-oil emulsion technique in which hydrolysis and condensation of tetraethyl siloxane and trimethoxysilylpropylmethacrylate take place. Spherical silica particles with a size range from 20 to 70 nanometers were obtained and the surface concentrations of the double bonds per square nanometer were from 4 to 7.
H. Yamauchi et al., "Surface Characterization of Ultramicro Spherical Particles of Silica Prepared by W/O Microemulsion Method, Colloids and Surfaces, vol. 37, pages 71 to 80 (1989), the disclosure of which is totally incorporated herein by reference, discloses the preparation of ultramicro spherical particles of colloidal silica by the hydrolysis of tetraethoxysilane in the water pool of a water-in-oil (isooctane) microemulsion using Aerosol-OT. The average diameter of the silica spheres obtained was of the order of 10 nanometers and their surface areas were about 100 to 300 square meters per gram. The nitrogen adsorption isotherms of this material showed that the particles have micropores, in contrast to colloidal nonporous silica particles such as aerosils and those in silica sols having a similar size of particle.
Copending application U.S. Ser. No. 07/495,669, filed Mar. 19, 1990, entitled "Toner Compositions Containing Colored Silica Particles," with the named inventors Francoise M. Winnik, David J. Luca, and Thomas W. Smith, discloses a toner composition which comprises a resin, hydrophilic silica particles having dyes covalently bonded to the particle surfaces through silane coupling agents, and a polymer having at least one segment capable of enhancing the dispersibility of the silica particles in the resin and at least one segment capable of adsorbing onto the surface of the silica particles. In one embodiment, the polymer segment capable of adsorbing onto the surface of the silica particles is ionophoric and capable of complexing with a salt, thereby incorporating a toner charge control additive into the polymer.
Copending U.S. application Ser. No. 07/369,003, filed Jun. 23, 1989, entitled "Inks and Liquid Developers Containing Colored Silica Particles," with the named inventors Francoise M. Winnik, Barkev Keoshkerian, Raymond W. Wong, Stephan Drappel, Melvin D. Croucher, James D. Mayo, and Peter G. Hofstra, discloses ink jet inks and liquid developers which contain colored particles comprising hydrophilic silica particles, to the surfaces of which dyes are covalently bonded through silane coupling agents. The ink jet inks generally comprise a liquid medium and a plurality of the colored silica particles. The liquid developers generally comprise a liquid medium, a resin, a plurality of the colored silica particles, and a charge control agent. The particles are prepared by a process which comprises reacting hydrophilic silica particles with a silane coupling agent in the absence of water to form particles having covalently attached thereto coupling agents, followed by reacting a dye with the coupling agent attached to the silica particles.
Although known compositions and processes are suitable for their intended purposes, a need remains for new colorant materials. In addition, a need remains for new colorant materials suitable for use in electrostatic toner compositions. Further, a need remains for colorants that are available in a wide variety of colors and that can be formulated in any desired color. There is also a need for colorant particles suitable for use in electrostatic toner compositions wherein colorant particles of different colors have similar triboelectric characteristics; generally, when known pigment particles are used as colorants in electrostatic toners, the pigments vary greatly in their triboelectric characteristics, so that interchangeable toners of different colors cannot be made simply by changing the pigment employed without varying other components of the developer. Additionally, there is a need for new colorant materials suitable for use in electrostatic toner compositions that exhibit a high degree of dispersion within the toner resin. Further, there is a need for new colorant materials suitable for use in electrostatic toner compositions that are of small particle size, thereby enabling formation of transparent colored toners that can be used to form images on transparencies for overhead projectors, wherein the projected images are of substantially the same color as the toner employed to form the image. There is also a need for colored particles which can be used to produce colored plastics by admixing the colorant particles with the plastic material. In addition, there is a need for colored particles which are suitable for use as colorants for liquid electrostatic developers. Further, there is a need for colored particles which are suitable for use as colorants for oil-based inks. Additionally, there is a need for colored particles which are suitable for use as colorants for hot melt ink jet inks.